Wind turbine generator systems generating electricity using wind power, which is natural energy, have been conventionally known. This type of wind turbine generator system includes a rotor head to which wind turbine rotor blades are attached, a main shaft coupled to the rotor head so as to integrally rotate with the rotor head, a speed-increasing gearbox coupled to the main shaft that rotates by means of wind power received by the wind turbine rotor blades, and a generator driven by shaft output power from the speed-increasing gearbox, which are provided in a nacelle mounted atop a tower.
In the thus-configured wind turbine generator system, the rotation of the main shaft and the rotor head provided with the wind turbine rotor blades that convert wind power to rotary power generates shaft output power. The output power of the shaft, whose rotational speed is stepped-up by the speed-increasing gearbox coupled to the main shaft, is transmitted to the generator. Accordingly, in the wind turbine generator system, the shaft output power obtained by converting wind power to rotary power works as the driving source of the generator, and thereby electricity can be generated using wind power as the motive energy of the generator.
The speed-increasing gearbox (speed-varying device) of the above-described wind turbine generator system is, for example, as shown in FIGS. 7 to 9, it is known a structure configured by combining parallel gears in which some pinion shafts (speed-varying shafts) are provided in a speed-varying stage that is provided between an input shaft and an output shaft. In addition, in the speed-increasing gearbox configured by combining spur gears, a reduction in weight is possible by employing a plurality of pinion shafts that are engaged with a gear wheel of a first stage.
In the speed-increasing gearbox 10 shown in the drawings, an input gear (gear wheel) 11 provided on an input shaft Si and an output gear (pinion) 12 provided on an output shaft So are coupled to each other via four pinion shafts Sv that are arranged in the circumferential direction. The pinion shafts Sv are each provided with gears 13 and 14, whose numbers of teeth are different from each other, at both ends.
That is, the pinion shafts Sv of the speed-increasing gearbox 10 are stepped up from the rotational speed of the input shaft Si according to the gear ratio between the input gear 11 and the gear 13 engaged with the input gear 11. Furthermore, the output shaft So of the speed-increasing gearbox 10 is stepped up from the rotational speed of the speed-varying shaft Sv according to the gear ratio between the gear 14 and the output gear 12 engaged with the gear 14 which is coaxial with the gear 13.
Consequently, the speed-increasing gearbox 10 shown in the drawings is a two-stage speed-increasing gearbox including a first stage for stepping-up the speed in which the rotational speed of the input shaft Si is stepped up to the rotational speed of the speed-varying shaft Sv and a second stage for stepping-up the speed in which the rotational speed of the speed-varying shaft Sv is stepped up to the rotational speed of the output shaft So.
In addition, as a speed-increasing gearbox of the above-mentioned wind turbine generator system, for example, there is one in which motive power is distributed into a plurality of power paths using parallel shaft gears in a low speed stage as a first stage, and each output shaft to which the motive power is distributed is coupled to a planetary gear (for example, see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. Hei 8-177711